The present invention relates generally to measuring systems for measuring the level of liquid held in a container. More specifically, the present invention relates to a measuring system that emits and receives ultrasonic signals and processes the ultrasonic signals to determine the level of liquid held in an underlying container and plays a major role in controlling operation of the system.
Devices for brewing coffee, especially while on board an aircraft, are well known in the industry. FIG. 1 is a block diagram portraying an airline coffee brewer typical in the prior art.
The prior art system includes a control board 10 that is normally constructed of discreet integrated circuits, input power from a 3-phase, 115 volt, 400 Hz aircraft power system 12, mechanical relay contacts 14, 16 and 18 that are actuated by coil 20 when coil 20 is energized with a signal 22 from control board 10. Mechanical relay contacts 14, 16 and 18 electrically isolate the low voltage control board 10 from the high voltage AC power lines supplying heating elements 24, 26 and 28. Heating elements 24, 26 and 28 are individually connected to the three phases of power system 12. A plurality of pot water level probes 30 are employed, in this example, as two free swinging metallic probes. Probes 30 come into contact with the water in the brewer when the carafe is full, as indicated at Level 4 and numeral 72 (FIG. 3). Probes 30 will momentarily swing out of the way when the carafe is inserted or removed from the brewer pocket. When probes 30 are in contact with the electrically conductive coffee in the carafe, a signal 32 occurs which will serve to close a cold-water input valve 34 that supplies cold water to boiler 39 which then heats it in preparation for brewing.
An additional probe, or sensor, 36 is located in boiler 39. Sensor 36, in conjunction with a processing circuit 37, that is external to boiler 39, will provide a control board input 38 when the boiler is filled with water. Sensor 36 and processing circuit 37 also serve to close relay contacts 14, 16 and 18 which provide power to heating elements 24, 26 and 28, which can be safely energized after the boiler is filled with water.
A temperature sensor 40 is also located in boiler 39. The external processing circuit 41 of temperature sensor 40 provides an input signal 42 to control board 10 when power to heating elements 24, 26 and 28 is needed in order to maintain a target temperature for the water.
One problem with the aforementioned prior art example is that the method for detecting a full carafe is subject to failure if sediment, carried by the water, forms on the sliding electrical surfaces of the probes 30. Another problem found in the prior art is that measuring intermediate levels of water in the container is either highly difficult, or not even possible. This will limit processor ability to determine other important performance characteristics of the brewer system. U.S. Pat. No. 5,880,364 (Dam) discloses a non-contact ultrasonic system for determining the volume of liquid in a container in which an ultrasonic sensor is disposed opposite the open top of the container. A circuit provides pulses of ultrasonic energy for transmission through the air to the air-liquid interface of liquid in the container and for measuring the round trip transit time from the sensor to the interface and back to the sensor. The system can determine the level of liquid in a plurality of containers using a plurality of sensors that are operated in sequence or simultaneously, or with a single sensor in which the plurality of sensors are moved relative to the single sensor for the volume of each of the sensors to be sequentially measured.
Regarding the ""364 patent, the components are not compactly located in the lid assembly of a container. The system of the present invention seeks to improve upon this system by presenting the ultrasonic transducers and their signal processing function in a lid assembly, thus making the system more compact, cost efficient, and resistant to splashing in turbulent conditions when used in aircraft or moving vehicles.
Thus, there is an unsatisfied need to realize a less complex, more cost efficient coffee brewing system having a significant increase in system reliability.
The present invention is directed to a system for measuring liquid levels in a container by means of an ultrasonic signal. The present invention is further directed to a system having all of the ultrasonic components located in the lid of the system. This design creates a more compact, cost efficient, lightweight and reliable system.
According to the present invention, a narrow ultrasonic beam is emitted from an ultrasonic signal transmitting transducer and directed to an underlying liquid column. The ultrasonic beam is reflected upward at the liquid/air interface to be detected by an ultrasonic signal receiving transducer that interfaces with a signal processor on the system. By knowing the speed of sound in air, the system is able to determine the exact distance traveled by the ultrasonic signal. In turn, by knowing the dimensions of the container, the exact amount of liquid within the container can be determined, or the liquid level in the container regardless of its dimensions. The present invention is described herein in the context of being used on board an aircraft, however, the present invention can be adapted to be employed in any other environment such as in household use, or on board any other type or mode of transportation, such as a train or cruise liner.
In one embodiment of the present invention, the mechanical relay contacts in each of the three AC lines of the prior art are replaced with an electrically isolated, optically coupled triac for controlling heater power. In this embodiment, the present invention allows for a single heating element to be direct current driven from the rectified three phase, 400 Hz alternating current power that is typical of aircraft systems. This design improves reliability and cost effectiveness of the system over the prior art.
It is an object of the invention to provide a brewing system that eliminates a typical mode of power failure associated with the prior art.
It is another object of the present invention to provide a brewing system that is more cost efficient, more space efficient, more lightweight and more reliable than the prior art.
It is yet another object of the present invention to provide a brewing system having all of the components compactly located in the lid assembly for measuring liquid level in a container.
Still yet another object of the present invention is to provide a brewing system having a single design for delivering power to the heating elements of both AC and DC aircraft power systems with very little design change.